Optical imaging techniques used in the prior art for observing atmospheric events that generate optical radiation in different wavelength bands were generally unable to produce images of a particular event in two or more wavelengths simultaneously. A typical technique of the prior art for observing such atmospheric events involved the use of filter wheels and time-sequencing filters as described in, e.g., and article by S. B. Mende et al. entitled "Instrument for the Monochromatic Observation of All Sky Auroral Images", Applied Optics, Vol. 16, No. 6, (June 1977), pages 1691-1700.
In general, filter wheel systems are inconveniently large, and require mechanical actuators and motors that are a significant encumbrance in severe conditions of climate and terrain (e.g., arctic and antarctic conditions) where observations of atmospheric events are of great interest. In addition, in using a filter wheel system for forming images of atmospheric events in different wavelengths, it is also necessary for an image-sequencing system to be coupled to the filter wheel system in order to record annotation data for each image produced. Without such annotation data, there would be no way to correlate a particular image with a particular wavelength. Furthermore, if the atmospheric events being observed involve time-variant phenomena, a comparative analysis of images formed at different times is likely to be plagued with artifacts unrelated to the actual events being observed.
A need had been perceived in the prior art for a technique that enables separate images of events that generate optical radiation (in particular, atmospheric events) to be formed simultaneously in two or more distinct wavelengths.